Electrically adjustable antenna technology is a common demand for present mobile communications system. This technology suitably changes phase of respective radiation elements of an antenna array by a phase shifter so as to adjust vertical beam steering of a base station antenna, thereby controlling application range of the base station. A phase shifter generally is capable of distributing an input signal into several branch output ports. Phase differences among these output ports may be regulated in ratio. With rapid development of mobile communications technology, the phase shifter should be designed to meet higher requirement. For example, it is required to have better broadband match performance, occupy even small space and so on. Extensive and various researches have been conducted by many researchers and designers to obtain a phase shifter with better performance and more effective structure.
By research and during development of the current invention, the inventor has found following problems in prior art.
U.S. Pat. No. 5,949,303 has disclosed a phase shifting method realized by moving a dielectric element 2 along a feeding network 1 of zigzag circular path. As shown in FIG. 1, when the zigzag circular path includes much more branch paths, as the edges of dielectric element intersect the feeding network at several locations, it has adverse effect on reduction of reflection signals and design of component with wide frequency band response. Moreover, the dielectric element covering respective branch paths must be moved simultaneously. As a result, the entire structural reliability and phase shifting accuracy of the phase shifter and transmission construction will be reduced. CN1547788A discloses a phase shifting device where phase shifting is realized by movement of an integral elongated dielectric plate disposed inside the device. The principle underlying this patent is similar to that of U.S. Pat. No. 5,949,303. Here, phase shift among several ports is achieved using multiple zigzag circular paths. In addition to difficulty in design of component with wide frequency band response such as ultra wide band phase shifter working at frequency range of 1710-2690 MHz, the phase shifting device located at the same plane and with multiple ports also occupies much space of the antenna, thus resulting in difficulty in reduce size of the antenna.
US20020030560 avoids above disadvantages but it employs a pie-shaped dielectric block 3 formed by sintering two dielectric pieces with different dielectric constant, as shown in FIG. 2. However, it suffers from drawbacks such as high manufacture cost, low production efficiency, thus being unsuitable for extensive application in industry. Moreover, to shift phase, pie-shaped dielectric block must take structure of rotatory transmission. As is well known, rotatory transmission structure is more complex than transmission structure of straight pulling type, thereby further limiting its application.